1. Field of the Invention
The invention relates to a method for determining an actuation position of a motor-driven adjusting element of a motor vehicle. It further relates to an actuator operating according to the method.
2. Description of the Background Art
In a modern motor vehicle, a number of actuators or adjusting elements operated by electric motors are usually present. These include, for example, an electric window regulator, an electric seat adjuster, and a device for motorized adjustment of a vehicle door, trunk lid, sunroof, or convertible top.
During an actuation process of such an adjusting element, it is frequently necessary to precisely move to a desired end position. A precise knowledge of the actuation position of the adjusting element is necessary for this purpose. The knowledge of the current actuation position or quantities that can be derived therefrom, such as the actuation speed or the travel that has been covered, are also frequently required for reliable detection of a pinch event or jamming.
For the most precise sensing of the actuation position of a window, it is known from, for example, DE 199 16 400 C1, which corresponds to U.S. Pat. No. 6,225,770, which is incorporated herein by reference, to provide a position and direction rotation sensor. This includes two Hall-effect sensors located offset from one another by a distance or angle, and a multipole, for example two-pole or four-pole, ring magnet located on the drive shaft of the electric motor. The Hall-effect sensors sense a magnetic field change resulting from a rotation of the ring magnet rigidly attached to the drive shaft and generate count pulses therefrom. These are analyzed in conjunction with information about the direction of rotation of the ring magnet, and hence of the electric motor, in that the count pulses are counted up or down depending on the direction of rotation of the drive, and thus indicate the current position of the window.
Integrated Hall-effect sensors are customarily employed for the sensor system, for example using CMOS (Complementary Metal Oxide Semiconductor) technology, which are integrated into a semiconductor chip (Hall IC) in addition to an analysis electronics unit, for example in ASIC (Application-Specific Integrated Circuit) technology together with the Hall-effect probes (DE 101 54 498 B4).
The Hall-effect probes can be understood as sensitive areas, for example as rectangular plates that are supplied with electrical energy in the form of a current or voltage source. In the presence of an external magnetic field perpendicular to this sensitive surface, a Hall voltage that is proportional to the magnetic flux density (induction) can be measured. A change in the magnetic flux density is also sensed by means of the Hall-effect sensor on the basis of the proportionality between the Hall voltage and the magnetic flux density. The Hall voltage change proportional thereto can then be analyzed accordingly as the sensor signal.
It is known from DE 10 2006 043 839 A1 to convert the magnetic field changes arising at the Hall-effect probes or Hall-effect sensors into two binary pulse trains, offset by 90° for example, in a comparator circuit with hysteresis (Schmitt trigger circuit). With such a comparator circuit with hysteresis, an upper switching threshold and a lower switching threshold are provided. By counting the pulses per unit of time, the rotational speed can be determined, while the direction of rotation of the electric motor or rotary drive is ascertained using a comparison of the two pulse trains.
As a result of the rotary motion of the ring magnet, its magnetic poles are alternately located directly opposite the end face of each sensitive Hall-effect area (Hall-effect probe), so that the magnetic field passing through this Hall-effect probe is oriented essentially orthogonal to the sensitive area. Accordingly, these orthogonal field components of the magnetic field and the Hall voltage proportional thereto are located in the vicinity of their maximum or minimum. In contrast, if the border between a north pole and a south pole of the ring magnet is located directly opposite the end face of this sensitive area, then the magnetic field passing through it is essentially parallel to the plane of the area, with the result that the Hall voltage becomes zero. As a function of the distance between the ring magnet and the Hall-effect areas of the Hall-effect sensor or Hall IC, the result is thus an at least approximately sinusoidal behavior of both the corresponding field component and the Hall voltage as a function of the angle of rotation.
When the relevant field component of the flux density (Hall voltage), which is sinusoidal as a function of the angle of rotation, exceeds the upper switching threshold, the pulse within the pulse train changes from a first logic level to a second logic level. This condition remains in effect until the relevant field component of the flux density, or the Hall voltage, negatively exceeds (falls below) the lower switching threshold.
Thus, the pulse train maintains the high level (logic 1), for example, both below the lower threshold and within the hysteresis between the two switching thresholds, until the upper switching threshold is exceeded again. Accordingly, the low level (logic 0) is maintained within the hysteresis until the lower threshold is negatively exceeded again. The upper switching threshold and the lower switching threshold are arranged symmetrically about the center line of the hysteresis, representing the zero crossing of the approximately sinusoidal curve of the magnetic flux density or the Hall voltage. The state definition under which a low level is prescribed above the upper switching threshold and a high level is always prescribed below that point is customary for a CMOS Hall-effect sensor.
In contrast, for an ideal sensor the region between a zero or center line within the hysteresis and the upper switching threshold is predefined as a low level, for example, while the region below the center line of the hysteresis to the lower switching threshold is predefined as a high level. Thus, in such an ideal sensor, the region above the upper switching threshold is assigned the low level, and the region below the lower switching threshold is assigned the high level.
Independently of the sensor concept, but in particular when a CMOS Hall-effect sensor is used in which a level change takes place when the upper threshold is positively exceeded and when the lower threshold is negatively exceeded, and a specific level, for example a high level, is prescribed within the hysteresis, states can arise that can lead to miscounting. Conditions leading to miscounting resulting from shifting of the switching thresholds of the Hall-effect sensor due to its self-heating or cooling, or a (slight) reverse rotation of the ring magnet subsequent to execution of a stop function of the electric motor, are extremely difficult to handle in this context. The danger of immediate miscounting of the Hall-effect sensor exists, in particular, after shutoff of the Hall-effect sensor or after restarting of a drive unit having the electric motor and ring magnet from an inactive phase (quiescent phase) when the switching thresholds have shifted as a result of temperature or operating conditions, and one pulse too many or too few is counted as a result.
To avoid miscounting, it is known from WO 2009/036972A2, which is incorporated herein by reference, to encode the switching states triggered by the changes in flux density or Hall voltage within the rotational-direction-dependent pulse train of the sensor output signal of the Hall-effect sensor by means of different pulse widths of the individual pulses.